1. Field of the Invention
This invention relates to an electric motor apparatus used for positioning a device such as robot arm along X-Y-Z axes, and more particularly, for a positioning device used for a television camera.
2. Description of the Prior Art
Positioning devices such as pan-tilt heads for television cameras or robot arms include a fixed body to be attached to a wall, a pole or a table and employs motors and power transmission assemblies consisting of gears or rollers or belts and pulleys or chains, and the like. Such pan-tilt heads or robot arm mechanisms are generally constructed so that the television cameras or the robot arm rotate angularly about their vertical and horizontal and/or other angular axes. In some cases electrical wires or a cable assembly are used for connecting the rotating television camera or the robot arm circuits to the fixed base of the positioning device. Such electrical wires or a cable are commonly known as a flexible cable assembly that spans between the fixed and the rotatable members, or between two rotatable members of the positioning device. The cable assembly thereby rotates and repeatedly twists or flexes along with the movement of the positioning device, and this eventually causes the cable to break. This requires a frequent cable replacement which is costly; moreover such cable assembly spanning across a joint of the positioning device prevents the positioning device from rotating over 360xc2x0 about its axis, which limits the free rotation of the positioning device.
Some positioning devices use slip-ring or rotating contact assemblies which are positioned at the individual rotating axis center, thereby eliminating the cable assemblies from spanning across the rotating joints. However, such slip ring assembly occupies the center of the rotating axis, thereby preventing the use of a direct drive motor, such as stepping motors, which are very efficient, accurate and require no power transmission mechanism.
It is an object of the present invention to provide a direct drive positioning device with a direct drive motor and a slip-ring mechanism mounted inside or along a main shaft of the motor. When such direct drive motor is positioned with its shaft at each axis, it permits a free unobstructed and continuous rotation, over 360xc2x0 in both horizontal and. vertical axes and/or other angular axes, with no cables twisting or flexing.
According to the present invention a direct drive positioning device comprises at least one rotating member for rotating about horizontal or vertical or any other angular axes of the positioning device. Each such rotating member is provided with means to mount a television camera or a robot arm and/or for mounting another member for incorporating a further joint positioning mechanism.
A direct drive motor has its central shaft connected to a rotating member for directly driving the rotating member wherein its central shaft comprises a rotating or slip ring assembly. The rotating contacts or the slip ring assembly provides for connecting the television camera, or the robot arm circuits and/or the direct drive motor circuit to a control circuit and other peripheral/ancillary equipment, thereby eliminating the problems associated with the use of flexing cables and providing for a continuous uninterrupted rotation about the rotating axis over 360xc2x0.